gnomeos: Make run script transparently update existing FS image

This is noticeably faster.

gnomeos/yocto/gnomeos-run.sh

@@ -49,41 +49,49 @@ if (! test -f ${OBJ}); then
     rm -f ${OBJ}.tmp
     qemu-img create ${OBJ}.tmp 2G
     mkfs.ext3 -q -F ${OBJ}.tmp
+    mv ${OBJ}.tmp ${OBJ}
+fi
+
 mkdir -p fs
 umount fs || true
-    mount -o loop ${OBJ}.tmp fs
+sleep 1 # Avoid Linux kernel bug, pretty sure it's the new RCU pathname lookup
+mount -o loop gnomeos-fs.img fs
 
 cd fs
 
 TOPROOT_BIND_MOUNTS="home root tmp"
 
 for d in $TOPROOT_BIND_MOUNTS; do
+    if ! test -d $d; then
         mkdir -m 0755 $d
+    fi
 done
 chmod a=rwxt tmp
 
+if ! test -d ostree; then
     mkdir ostree
     mkdir -p -m 0755 ./ostree/var/{log,run,tmp,spool}
+    mkdir ostree/repo
+    ostree --repo=ostree/repo init
+fi
 cd ostree
-    mkdir repo
-    ostree --repo=repo init
 ostree --repo=${OSTREE_REPO} local-clone repo
 for branch in base dev; do
     rev=$(ostree --repo=repo rev-parse ${BRANCH_PREFIX}${branch});
+    if ! test -d ${BRANCH_PREFIX}${branch}-${rev}; then
         ostree --repo=repo checkout ${rev} ${BRANCH_PREFIX}${branch}-${rev}
-        ln -s ${BRANCH_PREFIX}${branch}-${rev} ${BRANCH_PREFIX}${branch}-current
+    fi
+    ln -sf ${BRANCH_PREFIX}${branch}-${rev} ${BRANCH_PREFIX}${branch}-current
 done
 cd ..
 
-    mkdir proc # needed for ostree-init
+test -d proc || mkdir proc # needed for ostree-init
 cp -a ./ostree/${BRANCH_PREFIX}base-current/usr/sbin/ostree-init .
 
 cd ${WORKDIR}
 
 umount fs
 rmdir fs
-    mv ${OBJ}.tmp ${OBJ}
-fi
 
 ARGS="$@"
 if ! echo $ARGS | grep -q 'init='; then